A gerund is the -ing form of a verb used as a noun (Swimming is healthy), while an infinitive is the base form, usually with to (to swim) or, after certain verbs, bare (let it go). Both are non-finite verb forms that let one verb act as the complement of another, and choosing between them is one of the most error-prone areas of English Complementation.
The gerund nominalises a verb and can fill any noun slot: as subject (Reading relaxes me), as object (I enjoy reading), and after prepositions, where the -ing form is obligatory (good at cooking, interested in learning, before leaving). The to-infinitive expresses purpose, intention, or a not-yet-realised action (I came to help, hoping to win). The bare infinitive follows modal verbs (She can swim), let/make/have + object (made him apologise), and verbs of perception (I saw her leave).
The controlling verb dictates the form, and the patterns must largely be learned item by item:
| Pattern | Verbs | Example |
|---|---|---|
| verb + -ing | enjoy, avoid, finish, mind, suggest, consider, deny | She avoided answering. |
| verb + to-infinitive | want, hope, decide, agree, manage, refuse, promise | They decided to leave. |
| verb + object + to-infinitive | want, ask, tell, allow, persuade, expect | I asked her to wait. |
| verb + bare infinitive | let, make, help (+ object) | Let me explain. |
Some verbs take both forms but with a clear shift in meaning, which Swan (2016) treats as a core teaching point:
| Verb | + -ing | + to-infinitive |
|---|---|---|
| remember | recall a past act: I remember locking the door. | not forget a future duty: Remember to lock the door. |
| forget | fail to recall: I'll never forget meeting her. | fail to do: I forgot to call. |
| stop | cease an activity: He stopped smoking. | pause for a purpose: He stopped to smoke. |
| try | experiment: Try adding salt. | attempt something difficult: Try to finish it. |
| regret | be sorry about the past: I regret saying that. | be sorry to announce: We regret to inform you... |